Lonni Sue suffered a debilitating illness (encephalitis) that, though she survived, left her with an inability to make new memories and erased all but some basic long term memories. Yet she has been able to continue with her life, learn things (though she doesn't remember that she has learned them) and help doctors and scientists learn about how the brain works and how memories are made and stored.

I also found this a slightly disturbing book as it makes you look at how you would feel losing memories (though Lonni Sue doesn't realize she's lost memories most times so she is an incredibly happy person as every day is a new experience) and how would you deal if a family member, be it sibling, child, parent or partner were to suddenly fall ill and then not remember or be able to build new memories.